Some of the fakes were extremely obvious unless you are a brainwashed drone. Most fake shots were shown from the opposite direction so the actors body blocks the shot. Real injections were filmed from the near side where the needle enters the arm. Some really bad fakes had caps on needles, empty syringes with no needle, movie prop fake collapsible needles, etc. The easiest deception is a real shot of saline. This requires a lot of faith between people that know they are evil and have no problem killing each other.